President Barack Obama’s handling of the Syria crisis has allowed Syrian President Bashar al-Assad to come back from near-defeat, and empowered America’s enemies, a leading U.S. senator said Thursday.

“I hope that we’ll wake up to the fact that we have ignored one of the great sad stories in modern history,” Sen. Lindsey Graham, a member of the Armed Services committee, said during public remarks at the Hudson Institute think tank.

“The Assad regime is winning five years down the road,” the former Republican presidential contender said.

“To say otherwise is just crazy -- we had the guy on the ropes at a time when it would have mattered, when the entire national security team of President Obama said ‘go in, go in hard, train the Free Syrian Army that was still intact.’”

Instead, Obama “took a pass”, allowing a security vacuum to form in Syria that “has been filled by radical groups like ISIL” and emboldened Assad's allies, namely Russia and Iran, Graham said.

More than 250,00 people have been killed during the now five-year Syrian conflict, and millions more have been forced to flee their homes.

The Obama administration’s reliance on the YPG to combat Daesh is unlikely to result in the group’s ouster from its de facto Syrian capital, Raqaa, Graham said. “This strategy to take Raqaa back from ISIL using YPG fighters is not going to work,” he said.

“The Kurds [YPG] are signed up because they have no intention of taking Raqaa – they are trying to clean out their areas and deal ISIL a blow where they can, but if you think they’re going to go into Raqaa, Syria, clean out the place and hold it, you don’t understand what’s going on in the Middle East.”

During a recent trip to Turkey, Graham said Turkish officials were “very worried” about the U.S.’s support for the group. Noting that Turkey viewed the YPG as "cousins of the PKK" terrorist group, Graham told reporters during a press conference earlier in the day that he has held several discussions in the Senate regarding the shortcomings of the U.S. strategy.

"Turkey is of the view that this strategy will never destroy ISIL,” he said.

And the conflict continues to reverberate beyond the country’s borders as Daesh establishes affiliates throughout the region, including Egypt and increasingly in Libya, he said.

“The Sinai and Libya would not be where they are at today without Syria,” he said. “The war in Syria has tentacles, and those tentacles are growing.” Daesh’s rise in Egypt’s Sinai Peninsula has prompted security cooperation between Cairo and Israel on a level that Graham said he’d never seen.

Graham also said that every actor in the region, including the Egyptians, Saudis and Turks believe that "Syria is headed toward being a satellite state of Iran.” “And that is a non-starter," he added.

However, he said, the world should prepare for another wave of refugees even if the U.S.-led coalition is "successful" in pushing Daesh back or replacing Assad in Syria.

"One of the takeaways is that we don’t have a safe haven inside of Syria for regime refugees to go”, he said, referring to Syrian government supporters who may face persecution if Assad is removed from power.